1. Field of the Invention
The present disclosure generally relates to an image-taking apparatus and a control method therefor and, more particularly, to those capable of appropriately switching an image output mode when a maximum gain value is set.
2. Description of the Related Art
A human color vision characteristic serving as a sensitivity to a color and a human luminous efficiency characteristic serving as a sensitivity to brightness fall within a range from 380 nm to 780 nm, which is referred to as a visible range. Humans have little sensitivity in a longer wavelength range than 700 nm. Generally in an image-taking apparatus, an infrared ray cut filter (IRCF) for visibility correction, which does not pass a light beam in a near-infrared region, is provided ahead of an image-pickup sensor so that color reproducibility can match the human color vision characteristic.
However, under low illumination at which a subject luminance decreases, the IRCF is often removed from an optical path so that the light beam in the near-infrared region is passed through the optical path, to increase the sensitivity. When the light beam in the near-infrared region is passed through the optical path, however, a color balance is lost. Therefore, an imaging mode is switched from a color image (a Day mode) to a monochrome image (a Night mode). A switching method also includes a function of automatically switching between a Day mode and a Night mode, which is referred to as an auto Day/Night (hereinafter referred to as an ADN).
In a lens having no IRCF insertion/removal mechanism, for example, a varifocal lens, the sensitivity cannot be increased, but noise that affects a color component can be removed. Therefore, there is a camera for merely switching an imaging mode from a color image to a monochrome image. A threshold value of the subject luminance at the time of switching from the color image to the monochrome image is determined based on automatic exposure (AE) data (a shutter speed, an iris, automatic gain control (AGC), a screen luminance) of the camera.
In recent years, cameras including a unit for setting a maximum gain value have been available, so that a scene having a screen a large part of which is black, e.g., a night scene can be clearly photographed by limiting a gain value of an AGC circuit.
An image-taking apparatus discussed in Japanese Patent Application Laid-Open No. 2010-279061, for example, uses a method for switching a mode by inserting or removing an infrared cut filter according to a determination result of at least one of outputs from an imaging unit and a luminosity detection unit.
However, in the configuration of the image-taking apparatus discussed in Japanese Patent Application Laid-Open No. 2010-279061, a maximum gain value cannot be set. On the other hand, in the camera having a function of setting a maximum gain value that has attracted a demand from a user in recent years, a determination reference value is not appropriately set in response to an output change according to the setting of the maximum gain value. Therefore, a mode switching cannot be correctly performed.